Method of quenching pipe



ly 1964 R. s. MIDDLEMISS METHOD OF QUENCHING PIPE Filed NOV. 21, 1962INVENTOR ROBERT 6. MlDDLEM/SS A Home United States Patent 3,140,964METHOD OF QUENCHING PIPE Robelt G. Middlemiss, Greenock Heights, Pa.,assignor to United States Steel Corporation, a corporation of New JerseyFiled Nov. 21, 1962, Ser. No. 239,252 6 Claims. (Cl. 148-143) Thisinvention relates to the hardening of metal pipe by heating it above itstransformation temperature, then progressively quenching it at a ratesufficient to produce conversion to the desired metallurgical structure.More particularly, the invention relates to a method for obtaininguniform tensile strength in a length of pipe, especially at the trailingend thereof.

Metal pipe may be hardened by progressively quenching it from above itstransformation temperature by the method and apparatus of Scott PatentNo. 2,776,230. In accordance therewith, an axially moving length of pipeis heated progressively as required, in a sectional barreltype furnace.As it leaves the exit end of the furnace, the pipe progressively passesthrough a liquid-spray quenching ring or rings. The spray of uniformlydispersed droplets discharged at an acute angle to the pipe surface,effectively penetrates the steam film thereon and maintains a highcooling rate with a minimum of back flow along the pipe, which wouldcause pre-cooling .or injury to the furnace lining. Thus, when a pipe ofsteel containing about 30% C and 1.6% Mn is passed axially through afurnace and heated to its transformation range of about 1475 F. andthereafter passed axially through a liquid-spray quenching ring, thereis cooling at a rate such as to cause conversion of a greater portion ofthe steel to a martensitic structure. Since the spray is applied in thedirection of pipe travel, spray enters the open trailing end of the pipelength with resultant inside quenching. This inside quenching is oftentoo severe and causes the formation of quench cracks.

In many instances, inside quenching of the ends of pipe lengths presentsno problem, since the short quenchafi'ected end portion of the pipe iscut off. This however, is not always permissible. One example is a pipelength having thickened or upset ends. Here, the economics or minimumlength limit of an upset do not permit even a short end portion to becut oif. In fact, not much more than an end-facing operation can beperformed on a quench-hardened pipe length, to produce a salableproduct.

Covering the trailing end of a pipe length with a plate or other meanshas been found effective to keep out the spray. Towever, this means doesnot permit the formation of substantially all matensite in the trailingend. Rather, martensite is formed nearest the quench surface, thenbainite at approximately the mid-wall portion with increasing amounts offree ferrite toward the inside surface. The softer constituents,especially free ferrite, result in lower yield strengths and the productdoes not meet the required specifications.

It is therefore an object of this invention to overcome thesediflEiculties by the use of an improved form of cover plate secured tothe trailing end of a pipe length, specifically a cover plate having ahole therein.

A more specific object is to progressively quench harden metal pipesubstantially uniformly after continuously welding onto the trailing endof the pipe length, a thin plate having a relatively small hole in thecenter thereof.

In accomplishing these and other objects of the invention, I haveprovided an improved process and structure, a preferred form of which isshown in the accompanying drawing. The single figure is a horizontalsection showing the upset trailing end of a pipe length having welded3,140,964 Patented July 14, 1964 thereto a cover plate of invention.This end is leaving the exit end of a furnace and is about to enter aliquidspray quenching ring.

Except for the cover plate, the single figure of the drawing issubstantially the same as FIGURE 2 of Scott Patent No. 2,776,230, thebroad method and apparatus of which I employ, and to which reference maybe made. A pipe length 10 is progressively heated to its transformationrange in a furnace 11, then progressively passed through a liquid-sprayquenching ring or rings 13. Water or other quenching liquid undersuitable pressure is sup plied from any convenient source through a main14, branch pipes 15 and spaced headers 16 to quenching rings 13, spacedalong the axis 17 of pipe length 10 and normal thereto. Each ring 13 isfitted with a plurality of nozzles 18 spaced therearound. Each nozzleprovides a diverging spray of liquid droplets to the pipe surface, theaxes of the sprays constituting elements of an imaginary cone having itsapex substantially on the pipe axis.

Prior to the above described progressive heating and liquid-sprayquenching steps, a cover plate 19 is welded to the trailing end oflength 10 preferably with a continuous bead of weldment along theperiphery of the plate. Plate 19 has a vent hole 20 therein, preferablyin the center thereof and of a small diameter relative to the platediameter.

This arrangement has been found effective in quenchhardening apipelength substantially uniformly, especially where the end has anupset 21. The plate prevents water from entering the trailing end as itpasses through the quenching spray. The vent hole is essential forbetter heating and cooling. It allows flame and hot gases to enterduring heating. It allows hot air and gases to leave during quenchingand admits a controlled quantity of water to proved a cooling ratesufiicient to obtain the required metallurgical structure, withoutinitiating quench cracks.

The preferred thickness of the plate is about A thinner plate may burnthrough during welding. A thicker plate, because of the increased weightof metal may retard the required cooling rate of an upset pipe end. Theperiphery of the plate should be completedy welded to the end face ofthe pipe since, with a spot-welded plate, too much water may enter theend, causing quench cracks.

The diameter of the vent hole may vary with the size of the pipe. A venthole about 4" diameter is preferred for upset drill pipe in a size rangeof 3 /2" to 4 /2" O.D. For this size range of pipe a diameter hole hasbeen found too small to elfect the preferred transformation hardening; ahole has been found too large, in that it admits too much water. A venthole about diameter is preferred 5" and 5 /2" O.D. upset drill pipe.

In carrying out the method of my invention, using the apparatus of ScottPatent 2,776,230, a length of 4% O.D. internal upset drill pipecontaining about .30% C, 1.6% Mn, .15% Si, 35% Mo and .06% V, having awall thickness of .337", upset ends about 3%" long and .906" maximumwall thickness, had a 4%" diameter A steel plate welded throughout itsperiphery to one end of the pipe. The plate had a A diameter hole in itscenter. With the covered end trailing, the length was progressivelyheated to its transformation temperature of about 1475 F. and thereafterwater quenched. After quenching and before tempering, the hole wasenlarged by means of a pointed and tapered special steel hammer to about1" in diameter. This larger opening in the plate insured circulation ofhot gases during tempering (to secure uniform finished properties. Aftertempering, the length met specifications and exhibited a substantiallyuniform tensile strength of more than about 135,000 p.s.i. The coverplate was cut off in the customary end-facing operation, about /2 of theoriginal trailing end being removed due to welding fusement.

While the above example illustrates a preferred method of operation,other conditions of operation may be used without departing from thespirit of the invention. Any liquid spray directed at an acute angle tothe direction of pipe travel may be used, that is effective to producethe desired metallurgical properties in the main portion of a pipelength. The vent hole may be off center or may comprise a plurality ofsmaller spaced holes, more particularly with an axially rotating pipe.

An axial vent hole and a plurality of spray nozzles having their axesconstituting an imaginary cone with its apex on the pipe axis arepreferred, since then a simple change, viz., in the vent-hole diameter,is usually all that is necessary when operating conditions are varied.Some of these variations include a change in pipe diameter, wallthickness, metal chemistry, axial speed during heating and quenching,number of spray rings used and quenchliquid pressure.

Although I have disclosed herein the preferred practice of my invention,I intend to cover as well any change or modification therein which maybe made without departing from the spirit and scope of the invention.

I claim:

1. A method of hardening metal pipe comprising abutting against one endof a pipe a cover plate having a hole therein thereby to completely sealthe inside diameter opening of said pipe end, heating said length abovethe critical temperature by passing the length through a heating zonewith the covered end trailing, then as the length emerges from saidzone, passing it through a liquid-spray quenching ring, said hole beingdimensioned to dissipate heat from the inside of said trailing end tosuch an extent as to efiect transformation hardening therein.

2. A method as defined in claim 1 characterized by continuously weldingsaid plate to the end of the pipe length.

3. A method as defined in claim 1 characterized by said plate havingsaid hole substantially on the axis of said pipe.

4. A method as defined in claim 1 characterized by said liquid spraycomprising a plurality of circumferentially spaced, diverging sprays ofliquid, the axes of said sprays constituting elements of an imaginarycone having its apex substantially on the pipe axis.

5. A method as defined in claim 1 characterized by the trailing end ofsaid pipe length being upset.

6. A method of hardening metal pipe comprising continuously welding toone end of a length of pipe, the edge of a cover plate having an axialhole therein, thereby to completely seal the inside diameter opening ofsaid pipe end, heating said length above the critical temperature rangeby passing the length through a heating zone with the covered endtrailing, and passing it through a circumferentially spaced liquid spraydirected at an acute angle to the direction of pipe travel, said holebeing dimensioned to dissipate heat from the inside of said trailing endto such an extent as to effect transformation hardening therein.

References Cited in the file of this patent UNITED STATES PATENTS709,631 Hadfield Sept. 23, 1902 2,776,230 Scott Jan. 1, 1957 2,804,412Anderson Aug. 27, 1957 UNITED STATES PATENT QFFICE CERTIFICATE OFCORRECTION Patent N0:c 3 140 964 July 14L 1964 Robert. Go Middlemiss nthe above numbered pat- It is hereby certified that error appears ishould read as erit requiring correction and that the said LettersPatentcorrected below.

,ior 'Towever" read However-{ Column 1 line 51.

035% line 57 column 2 line 56 for '35% "Jread"-= after "5906"" insert,in 5? Signed and sealed this 10th day of November 1964;

(SEAL) Attest:

ERNEST w. SWI-DER v EDWARD J. BRENNER Commissioner of Patents AttestingOfficer

1. A METHOD OF HARDENING METAL PIPE COMPRISING ABUTTING AGAINST ONE ENDOF A PIPE A COVER PLATE HAVING A HOLE THEREIN THEREBY TO COMPLETELY SEALTHE INSIDE DIAMETER OPENING OF SAID PIPE END, HEATING SAID LENGTH ABOVETHE CRITICAL TEMPERATURE BY PASSING THE LENGTH THROUGH A HEATING ZONEWITH THE COVERED END TRAILING, THEN AS THE LENGTH EMERGES FROM SAIDZONE, PASSING IT THROUGH A LIQUID-SPRAY QUENCHING RING, SAID HOLE BEINGDIMENSIONED TO DISSIPATE HEAT FROM THE INSIDE OF SAID TRAILING END TOSUCH AN EXTENT AS TO EFFECT TRANSFORMATION HARDENING THEREIN.